Of all the things I'd say about Paper Jam I wouldn't even call its art direction uninspired, it's the same gorgeous art-style they used in Dream Team. The enemy selections aren't the most diverse if that's what you mean but I really loved how different the paper and real enemies were, particularly when it comes to the boss fights and other such things (Paper Petey was so different from regular Petey, also Petey Piranha should be in more Mario things, I want to golf with real power again.)
Maybe I just don't get it, I agree NSMB as an art direction is getting old (I appreciate their Van Gogh painting level though that was kinda cool) but Paper Jam never struck me as that.
The only game I was disappointed in when it comes to spin-offs is Ultra Smash tbh, that game deserved to be good but they rushed the **** out of Camelot and it wasn't the Mario Golf World Tour of Mario Tennis games.